North Atlantic Polar Front Research Articles

British–Irish Ice Sheet and polar front history of the Goban Spur, offshore southwest Ireland over the last 250 000 years

Deep Sea Drilling Program (DSDP) Site 548 was cored in 1984 at a water depth of 1256 m on the Goban Spur, offshore southwest Ireland. Coring retrieved a ~100‐m‐thick Pleistocene contourite sequence. This study uses planktonic foraminiferal assemblage and benthic foraminiferal oxygen isotope analyses to establish an age model for the upper 40 m of this core. This site's multidisciplinary analyses of planktonic foraminiferal assemblages, lithic grains, facies and calcium carbonate concentration reveal a 250 000‐year record of the North Atlantic polar front variability and British–Irish Ice Sheet (BIIS) history. The sequence is characterized by alternations of ice rafted debris (IRD) laden pelagic mud facies with calcium carbonate‐rich silty sand contourite facies that track glacial/interglacial cycles. The polar front migrated southward across the area several times during glacial maxima and stadial periods, while warmer Mediterranean Outflow Water (MOW) flowed northward across the region during interglacial and interstadial periods depositing contourites. Lithic analyses reveal a complex history of IRD deposition associated with iceberg calving from the Laurentide Ice Sheet and northwest European ice sheets, mainly the BIIS. Comparison between the Goban Spur (DSDP Site 548) and the Celtic Margin (MD03‐2692) and central North Atlantic Integrated Ocean Drilling Program (IODP) Site U1308 suggests differences between the ‘non‐Laurentide Ice Sheet’ Heinrich Events (HE) 6 and 3 at the Goban Spur, with IRD from the BIIS being prominent during HE 6 and IRD from other European ice sheets north of the BIIS likely being more dominant during HE 3. The nature of lithics in IRD‐rich horizons during Terminations 3, 3A, 2 and 1 suggests significant iceberg calving episodes preceding BIIS retreat during the onset of interstadial intervals.

Hydroclimatic changes in the British Isles through the Last-Glacial-Interglacial Transition: Multiproxy reconstructions from the Vale of Pickering, NE England

European paleoenvironmental records through the Last Glacial-Interglacial Transition (LGIT; ca 16-8 cal ka BP) record a series of climatic events occurring over decadal to multi-centennial timescales. Changes in components of the climatic system other than temperature (e.g. hydrology) through the LGIT are relatively poorly understood however, and further records of hydroclimatic changes are required in order to develop a more complete understanding on the phasing of environmental and anthropogenic responses in Europe to abrupt climate change. Here, we present a multiproxy palaeoenvironmental record (macroscale and microscale sedimentology, macrofossils, and carbonate stable isotopes) from a palaeolake sequence in the Vale of Pickering (VoP), NE England, which enables the reconstruction of hydroclimatic changes constrained by a radiocarbon-based chronology. Relative lake-level changes in the VoP occurred in close association (although not necessarily in phase) to threshold shifts across abrupt climate change transitions, most notably lowering during cooling intervals of the LGIT (∼GI-1d, ∼GI-1b, and ∼GS-1). This reflects more arid hydroclimates associated with these cooling episodes in the British Isles. Comparisons to hydrological records elsewhere in Europe show a latitudinal bifurcation, with Northern Europe (50–60°N) becoming more arid (humid), and Southern Europe (40–50°N) becoming more humid (arid) in response to these cooling (warming) intervals. We attribute these bifurcating signals to the relative positions of the Atlantic storm tracks, sea-ice margin, and North Atlantic Polar Front (NAPF) during the climatic events of the LGIT.

A revised chronology for the growth and demise of Loch Lomond Readvance (‘Younger Dryas’) ice lobes in the Lochaber area, Scotland

We present a revised varve chronology for the duration of ice-dammed lakes that formed in the Lochaber district, Scotland, during the Loch Lomond (‘Younger Dryas’) Stadial. We analysed new varved sequences and combined them with existing varve records to develop the Lochaber Master Varve Chronology 2019 (LMVC19), published here for the first time. It spans an interval of 518 ± 18 vyrs and is considered more secure than its predecessors because: (i) it is anchored by a more robust record of the Vedde Ash, which is dated to 12,043 ± 43 cal yr BP; and (ii) it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently-dated, non-varved records obtained from neighbouring sites. The new results indicate that the Lochaber ice-dammed lakes existed between ∼12,135 and 11,618 ± 61 cal yr BP, but the pattern of glacier advance that led to lake formation was more complex than previously assumed, with some ice fronts reaching their maximal positions 300 years before others. Initiation of ice retreat at ∼11,800 cal yr BP appears to have coincided with a rise of ∼2 °C in mean July temperatures inferred from chironomid data obtained from the Abernethy Forest site in the eastern Highlands. This local climatic shift is thought to have been a delayed response (by up to 335 years) to a mid-Stadial northward migration of the North Atlantic Polar Front, the delay probably due to the influence of the SW Highland icefield. Subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of ∼3 °C at the start of the Early Holocene. Final drainage of the lake system occurred ∼190 years after the initiation of ice retreat, while it took a further 200 years for the ice to vacate the Rannoch plateau, a nearby upland glacial source.

Paleocurrents in the Charlie-Gibbs Fracture Zone during the Late Quaternary

Planktonic foraminiferal and ice-rafted debris count data, as well as the mean size of mineral particles of the 10–63 μm fraction (sortable silt, $$\overline {SS} $$ ) were used as a proxy for surface and near-bottom paleocurrent intensity variations. The data obtained support our hypothesis about turbiditic origin of the lower (80–370 cm) section of the studied AMK-4515 core. Stratigraphic subdivision of the upper section (0–80 cm) makes it possible to allocate two marine isotope stages (MIS) covering the last 27 ka. The main intervals of the North Atlantic Polar Front (PF) migrations were recorded: south of the modern PF position during early MIS 2 (24–27 ka) with PF presence in the study area during MIS 2 (20–24 ka); south of the study area during the last glacial maximum (18–20 ka). Influence of the near-bottom currents within the investigated interval led to beginning of the channel-related drift formation on the northern slope of the southern channel of the Charlie-Gibbs Fracture Zone. There is a weak relationship between intensity of near-bottom contour currents and long-term climatic cyclicity. However, intervals corresponding to Heinrich events coincide with decrease in bottom currents activity.

Drivers and potential predictability of summer time North Atlantic polar front jet variability

The variability of the North Atlantic polar front jet stream is crucial in determining summer weather around the North Atlantic basin. Recent extreme summers in western Europe and North America have highlighted the need for greater understanding of this variability, in order to aid seasonal forecasting and mitigate societal, environmental and economic impacts. Here we find that simple linear regression and composite models based on a few predictable factors are able to explain up to 35 % of summertime jet stream speed and latitude variability from 1955 onwards. Sea surface temperature forcings impact predominantly on jet speed, whereas solar and cryospheric forcings appear to influence jet latitude. The cryospheric associations come from the previous autumn, suggesting the survival of an ice-induced signal through the winter season, whereas solar influences lead jet variability by a few years. Regression models covering the earlier part of the twentieth century are much less effective, presumably due to decreased availability of data, and increased uncertainty in observational reanalyses. Wavelet coherence analysis identifies that associations fluctuate over the study period but it is not clear whether this is just internal variability or genuine non-stationarity. Finally we identify areas for future research.

Younger Dryas sea level and meltwater pulse 1B recorded in Barbados reef crest coral Acropora palmata

AbstractThe Younger Dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the North Atlantic polar front almost to its former glacial position, trending east to west. Using high‐precision and high‐accuracy U‐Th‐dated Barbados reef crest coral, Acropora palmata, we generate a detailed sea level record from 13.9 to 9000 years before present (kyr B.P.) and reconstruct the ice volume response to the Younger Dryas cooling. From the mid‐Allerød (13.9 kyr B.P.) to the end of the Younger Dryas (11.65 kyr B.P.), rates of sea level rise decreased smoothly from 20 mm yr−1 to 4 mm yr−1, culminating in a 400 year “slow stand” before accelerating into meltwater pulse 1B (MWP‐1B). The MWP‐1B event at Barbados is better constrained as beginning by 11.45 kyr B.P. and ending at 11.1 kyr B.P. during which time sea level rose 14 ± 2 m and rates of sea level rise reached 40 mm yr−1. We propose that MWP‐1B is the direct albeit lagged response of the Northern Hemisphere ice sheets to the rapid warming marking the end of the Younger Dryas coinciding with rapid warming in the circum‐North Atlantic region and the polar front shift from its zonal to meridional position 11.65 kyr B.P. As predicted by glaciological models, the ice sheet response to rapid North Atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets. The regional circum‐North Atlantic Younger Dryas climate event is elevated to a global response through sea level changes, starting with the global slowdown in sea level rise during the Younger Dryas and culminating with MWP‐1B. No meltwater pulses are evident at the initiation of the Younger Dryas climate event as is often speculated.

Migrations of the North Atlantic Polar front during the last 300 ka: Evidence from planktic foraminiferal data

Polar front (PF) migrations were reconstructed for middle latitudes of the North Atlantic during the last 300 000 using planktic foraminiferal census data and derived from them sea surface temperature (SST) estimates in two sediment cores, AMK-4438 and M23414. Currently both investigated sites underlie the North Atlantic Current (NAC). Faunal results were supported by stable isotopic and IRD data. It was found that the arctic waters had propagated to the study area only during glacial winter seasons of MIS 2, 6, and 8. The northern part of the study area was influenced by the arctic waters more often than its southern part. During MIS 8 and 6 isotherms in the study area had mainly the subzonal orientation, while during MIS 2-4 they had the submeridional orientation. In general, during the investigated interglaciations, PF was located northward and westward from the study area, which was influenced by NAC. However, during MIS 7, PF was situated closer to the study area, in comparison with its modern position. During MIS 7 and 1, the subzonal orientation of the isotherms prevailed. For the MIS 5e period, we observed the most distant retreat of PF from the investigated area, which is in accordance with previous investigations reporting an anomalous deflection of NAC to the north-west.

Drivers of North Atlantic Polar Front jet stream variability

ABSTRACTPolar front jet stream variability is responsible for instances of extreme weather and is crucial for regional climate change. The North Atlantic Polar Front jet stream is of particular significance to the heavily populated areas of western Europe and eastern North America as storm track variability, atmospheric modes of variability such as the North Atlantic Oscillation (NAO), temperature and rainfall are all intimately linked with jet stream changes. Although seasonal and interannual variability are often attributed to internal variability, there are several possible drivers of polar front jet stream changes that are reviewed in this study. Cryospheric effects from sea‐ice extent and snow cover, oceanic effects from North Atlantic sea‐surface temperatures and tropical influences such as the El‐Niño Southern Oscillation, and stratospheric effects due to stratospheric circulation variability, solar variability, volcanic eruptions and the Quasi‐Biennial Oscillation are all identified in the literature as factors that impact on the Atlantic Polar Front jet stream. These drivers of jet stream variability can oppose or reinforce one another, and there are some indications of possible nonlinear interactions between them. We also review the modelling of jet stream variability. While a consensus has now been reached that some observed drivers can be reproduced in climate models, we conclude that improved understanding of more recently identified drivers of the Atlantic extratropical jet stream is crucial for making progress in regional climate predictions on all timescales from months to decades ahead.

Migrations of the North Atlantic Polar Front during the Last 300 ka: Evidence from Planktic Foraminiferal Data

Migrations of the North Atlantic Polar Front during the Last 300 ka: Evidence from Planktic Foraminiferal Data

Early maximum extent of paleoglaciers from Mediterranean mountains during the last glaciation

Mountain glaciers respond directly to changes in precipitation and temperature, thus their margin extent is a high-sensitivity climate proxy. Here, we present a robust 10Be chronology for the glacier maximum areal extent of central Spain paleoglaciers dated at 26.1 ± 1.3 ka BP. These glaciers reached their maximum extent several thousand years earlier than those from central Europe due to the increased precipitation within a cold period between 25 to 29 ka BP, as confirmed by a local speleothem record. These paleoclimate conditions impacted the maximum extent of mountain glaciers along the western and central Mediterranean region. The cause and timing of the enhanced precipitation implies a southward shift of the North Atlantic Polar Front followed by storm tracks in response to changes in insolation via orbital parameters modulation. Thus, these mountain paleoglaciers from the Mediterranean region record an ocean-continent climate interaction triggered by external forcing.

Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica

A multicentennial and absolutely-dated shell-based chronology for the marine environment of the North Icelandic Shelf has been constructed using annual growth increments in the shell of the long-lived bivalve clam Arctica islandica. The region from which the shells were collected is close to the North Atlantic Polar Front and is highly sensitive to the varying influences of Atlantic and Arctic water masses. A strong common environmental signal is apparent in the increment widths, and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95% confidence level, they are low (r~0.2), indicating that a more complex combination of environmental forcings is driving growth. Remarkable longevities of individual animals are apparent in the increment-width series used in the chronology, with several animals having lifetimes in excess of 300years and one, at 507years, being the longest-lived non-colonial animal so far reported whose age at death can be accurately determined. The sample depth is at least three shells after AD 1175, and the time series has been extended back to AD 649 with a sample depth of one or two by the addition of two further series, thus providing a 1357-year archive of dated shell material. The statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age-related trend in shell growth. Comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales, particularly during the period surrounding the transition from the Medieval Climate Anomaly to the Little Ice Age.

Growth, dynamics and deglaciation of the last British–Irish ice sheet: the deep-sea ice-rafted detritus record

The evolution and dynamics of the last British–Irish Ice Sheet (BIIS) have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data. This reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary. In order to enhance BIIS reconstruction, we present a compilation of new and previously published ice-rafted detritus (IRD) flux and concentration data from high-resolution sediment cores recovered from the NE Atlantic deep-sea continental slope adjacent to the last BIIS. These cores are situated adjacent to the full latitudinal extent of the last BIIS and cover Marine Isotope Stages (MIS) 2 and 3. Age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera Neogloboquadrina pachyderma sinistral (% Nps) to the Greenland GISP2 ice core record. Multiple IRD fingerprinting techniques indicate that, at the selected locations, most IRD are sourced from adjacent BIIS ice streams except in the centre of Heinrich (H) layers in which IRD shows a prominent Laurentide Ice Sheet provenance. IRD flux data are interpreted with reference to a conceptual model explaining the relations between flux, North Atlantic hydrography and ice dynamics. Both positive and rapid negative mass balance can cause increases, and prominent peaks, in IRD flux. First-order interpretation of the IRD record indicates the timing of the presence of the BIIS with an actively calving marine margin. The records show a coherent latitudinal, but partly phased, signal during MIS 3 and 2. Published data indicate that the last BIIS initiated during the MIS 5/4 cooling transition; renewed growth just before H5 (46 ka) was succeeded by very strong millennial-scale variability apparently corresponding with Dansgaard–Oeschger (DO) cycles closely coupled to millennial-scale climate variability in the North Atlantic region involving latitudinal migration of the North Atlantic Polar Front. This indicates that the previously defined “precursor events” are not uniquely associated with H events but are part of the millennial-scale variability. Major growth of the ice sheet occurred after 29 ka with the Barra Ice Stream attaining a shelf-edge position and generating turbiditic flows on the Barra–Donegal Fan at ∼27 ka. The ice sheet reached its maximum extent at H2 (24 ka), earlier than interpreted in previous studies. Rapid retreat, initially characterised by peak IRD flux, during Greenland Interstadial 2 (23 ka) was followed by readvance between 22 and 16 ka. Readvance during H1 was only characterised by BIIS ice streams draining central dome(s) of the ice sheet, and was followed by rapid deglaciation and ice exhaustion. The evidence for a calving margin and IRD supply from the BIIS during Greenland Stadial 1 (Younger Dryas event) is equivocal. The timing of the initiation, maximum extent, deglacial and readvance phases of the BIIS interpreted from the IRD flux record is strongly supported by recent independent data from both the Irish Sea and North Sea sectors of the ice sheet.

A 4500-year reconstruction of sea surface temperature variability at decadal time-scales off North Iceland

Marine paleo-records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability. This study presents a unique 4500-year reconstruction of sea surface temperature (SST) obtained from alkenones in the North Atlantic Polar Front area off North Iceland, at an average temporal resolution of 4–5 years. Spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years BP, hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies. Contemporaneous large excursions of the Inter-tropical Convergence Zone (ITCZ) are also recorded by the distant Cariaco titanium time series, suggesting a link with low latitude Atlantic climate. We speculate that the oscillations reflect changes of the Meridional Overturning Circulation (MOC) induced by increased ENSO activity.

Rodent paleofaunas as indicators of climatic change in Europe during the last 125,000 years

This paper presents a quantitative reconstruction of the European late Pleistocene paleoclimate based on 72 rodent assemblages of five sequences from France, Germany and Bulgaria, covering the last interglacial–glacial cycle. They show a pattern of severe changes in temperature, with reduced precipitation during the coldest periods. A tentative correlation between the isotopic and palynological records and the paleotemperature changes is shown. These changes are consistent with variations in atmospheric circulation patterns in response to an expanding–retracting Fennoscandian ice-sheet. They can be attributed to the enhancement–weakening of the Scandinavian-Polar anticyclone and its associated dry winds, the south–north shifting of the North Atlantic Polar Front, and the varying supply of moist air from the Atlantic. Qualitative paleoenvironmental analysis shows broadleaved-deciduous forests in France and Bulgaria during most of the studied period. Taiga and tundra appeared in eastern France during the lower Würm. The German sequence indicates the presence of coniferous forests. These results are broadly consistent with other paleobiological records (mammalian, avian and insect faunas, isotopic record in dental tissue, palynology). The main discrepancies with the paleoclimate inferred from the palynological record are found during the coldest periods and are probably due to the interaction between vegetation, climate, and atmospheric CO 2 levels.

North Atlantic warming during global cooling at the end of the Cretaceous

Research Article| June 01, 2005 North Atlantic warming during global cooling at the end of the Cretaceous Kenneth G. MacLeod; Kenneth G. MacLeod 1Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211-1380, USA Search for other works by this author on: GSW Google Scholar Brian T. Huber; Brian T. Huber 2Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20013-7012, USA Search for other works by this author on: GSW Google Scholar Carolina Isaza-Londoño Carolina Isaza-Londoño 3Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211-1380, USA Search for other works by this author on: GSW Google Scholar Geology (2005) 33 (6): 437–440. https://doi.org/10.1130/G21466.1 Article history received: 14 Dec 2004 rev-recd: 08 Feb 2005 accepted: 10 Feb 2005 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Kenneth G. MacLeod, Brian T. Huber, Carolina Isaza-Londoño; North Atlantic warming during global cooling at the end of the Cretaceous. Geology 2005;; 33 (6): 437–440. doi: https://doi.org/10.1130/G21466.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Differences in regional responses to climate fluctuations are well documented on short time scales (e.g., El Niño–Southern Oscillation), but with the exception of latitudinal temperature gradients, regional patterns are seldom considered in discussions of ancient greenhouse climates. Contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years, this paper shows that the North Atlantic warmed by as much as 6 °C (1.5‰ decrease in δ18O values of planktic foraminifera) during the Maastrichtian global cooling interval. We suggest that warming was the result of the importation of heat from the South Atlantic. Decreasing North Atlantic δ18O values are also associated with increasing gradients in planktic δ13C values, suggesting increasing surface-water stratification and a correlated strengthening of the North Atlantic Polar Front. If correct, this conclusion predicts arctic cooling during the late Maastrichtian. Beyond implications for the Maastrichtian, these data demonstrate that climate does not behave as if there is a simple global thermostat, even on geologic time scales. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Thermal gradients in Europe during the last glacial-interglacial transition

AbstractTemperature profiles along east-west and north-south transects in Europe are presented for four time-slices covering the two most prominent warming phases of the last glacial-interglacial transition: Late Pleniglacial (LP), early Bøiling (BL), Younger Dryas (YD), and Preboreal (PB). These temperature profiles are based on two methods: 1) simulation experiments with an atmospheric general circulation model, 2) reconstructions based on terrestrial geological and palaeoecological data. The profiles have The Netherlands as intersection point (52°N, 5°E). During the cold phases (LP and YD), the simulated and reconstructed temperature gradients are very steep in a north-south direction, ranging in January from -25°C in northern Europe (56–60°N) to at least 5°C near the Mediterranean, and in July from 0°C to 20°C. The east-west profiles along 52°N for LP and YD show that temperatures in Eastern Europe were similar to the Atlantic coast (i.e. between ‒15°C and ‒25°C). During the warm phases (BL and PB), the temperature regimes resembled present-day thermal conditions, although steeper north-south and east-west temperature gradients were present during BL and PB. The model simulations suggest that continental Europe was a few degrees warmer during PB and BL than today in July under influence of the relatively high summer insolation. Considering the change of climate through time, the profiles show that in The Netherlands the warming during the two transitions (LP-BL, YD-PB) was relatively small compared to regions to the West and North, whereas in Eastern and Southern Europe the temperature increase is even smaller. This reflects the dominant influence of latitudinal movements of the North Atlantic polar front and associated sea-ice margin.

North Atlantic sea-surface temperature changes and the climate of western Iberia during the last deglaciation; a marine palynological approach

Sea-surface temperature (SST) variations based on δ 18O and dinoflagellate cyst records in core SO75-6KL indicate that shifts in the position of the North Atlantic polar front during the last deglaciation led to sudden changes of the SST in the offshore area of Portugal. Our data show that the onset of the two major cooling events, attributed to Heinrich event 1 (H1) and the Younger Dryas (YD), occurred within 600 and 400 years, respectively. The first-order land–sea correlation, provided by the pollen record of SO75-6KL, enables a detailed evaluation of the response of the vegetation on land to altered heat and moisture transport from the North Atlantic Ocean toward SW Europe. The expansion of aridity-tolerant vegetation, as reflected in the pollen record of steppe taxa, occurred within 350 and 180 years from the onset of the cooling events connected to H1 and the YD, respectively. The inception of the warmer interval assigned to the Bølling-Allerød Interstadial shows a less sudden response, probably due to competition or to the lower migration rates for deciduous trees such as Quercus compared to most steppe taxa.

Variability of the western Mediterranean Sea surface temperature during the last 25,000 years and its connection with the Northern Hemisphere climatic changes

Sea surface temperature (SST) profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a W‐E latitudinal transect encompassing the Gulf of Cadiz (Atlantic Ocean), the Alboran Sea, and the southern Tyrrhenian Sea (western Mediterranean). The results document the sensitivity of the Mediterranean region to the short climatic changes of the North Atlantic Ocean, particularly those involving the latitudinal position of the polar front. The amplitude of the SST oscillations increases toward the Tyrrhenian Sea, indicating an amplification effect of the Atlantic signal by the climatic regime of the Mediterranean region. All studied cores show a shorter cooling phase (700 years) for the Younger Dryas (YD) than that observed in the North Atlantic region (1200 years). This time diachroneity is related to an intra‐YD climatic change documented in the European continent. Minor oscillations in the southward displacement of the North Atlantic polar front may also have driven this early warming in the studied area. During the Holocene a regional diachroneity propagating west to east is observed for the SST maxima, 11.5–10.2 kyr B.P. in the Gulf of Cadiz, 10–9 kyr B.P. in the Alboran Sea, and 8.9–8.4 kyr B.P. in the Thyrrenian Sea. A general cooling trend from these SST maxima to present day is observed during this stage, which is marked by short cooling oscillations with a periodicity of 730±40 years and its harmonics.

Extent of permafrost in southern Britain in relation to geothermal flux

Introduction The scarcity of relic permafrost features in southwest England, except on the high ground of Dartmoor, was noted by Williams (1965, 1969). Following Manley (1951, 1953) he concluded that this was due primarily to a moderation of the Pleistocene climate by invasions of milder Atlantic air. Subsequent work through the CLIMAP project ( McIntyre et al 1976 ), however, suggests that at 18000 years BP, the North Atlantic polar front was at about the latitude of Portugal. Comparison of Williams' map of the areal extent of permafrost in southern Britain with the detailed heat flow map of the UK ( Wheildon & Rollin 1986 ) indicates that regions where evidence of former permafrost is largely absent tend to coincide with areas of high heat flow. The technical note discusses possible relationships between heat flow and permafrost phenomena in southern England as it is clearly important that engineers making site assessments are aware of the likely causes and extent of the disturbance associated with former frozen ground. Extent and depth of former permafrost in southern Britain Figure la is a reproduction of Williams' (1969) map which was based on the deeper periglacial features, particularly ice-wedge casts. It shows that there are far fewer permafrost features in the southwest than in most of Britain. Since then more ice-wedge casts have been found in southwest England, but it is nevertheless generally accepted that in this area the frequency and depth of these is significantly less than

Late Pleistocene Southern Ocean δ13C variability

Variations in the contribution of North Atlantic Deep Water (NADW), relative to North Pacific Deep Water (NPDW), to the Southern Ocean, are assessed by comparing δ13C records from the mid‐depth North Atlantic, deep Southern Ocean, and deep equatorial Pacific Ocean. In general, the relative contribution of NADW was greater during interglaciations than glaciations of the past 550,000 years. An increase in the NADW flux to the Southern Ocean since the last glaciation was proposed to have resulted in higher atmospheric CO2 in the Holocene (Broecker and Peng, 1989). Glacial‐interglacial variations in the proportion of NADW in the Southern Ocean may have also influenced atmospheric CO2 levels over the past 550,000 years. The greatest relative flux of NADW to the Southern Ocean occurred during interglacial stage 11. Faunal data suggest that the North Atlantic polar front and southern Indian Ocean subtropical convergence zone were located farthest poleward during stage 11. Warmth in these locations and a strong southward flux of NADW during stage 11 may be causally linked by the NADW formation process/warm water return route (Gordon, 1986). Time series analysis indicates that δ13C variations in the deep Southern Ocean occur at the same frequencies as the Earth's orbital variations and are coherent and in phase with δ18O. At most, 50% of the glacial‐interglacial δ13C amplitude in the Southern Ocean is due changes in the contribution of NADW. The remainder is probably due to mean ocean δ13C changes.